This invention pertains to a vibration-isolating mounting for absorbing vibrations transmitted from a machine, such as an engine, to a supporting structure. More particularly, it pertains to a novel bushing-sleeve combination used for such a purpose.
Resilient elastomeric bushings, used in combination with central metal sleeves, have long been employed as vibration-isolating devices for mounting, as an example, an engine on a supporting frame, or similar structure. The typical bushing includes an elongate cylindrical body, with a flange portion projecting radially outwardly from one end thereof. The bushing has a continuous bore of uniform diameter, axially centered in the cylindrical body, which bore receives a hollow, cylindrical, metal sleeve. The sleeve has a shorter length than the bore, in order to accommodate sufficient bushing compression and compacting during mounting.
A typical engine-mounting procedure, using such a combination, first involves placing such a bushing through the top side of an aperture in the support structure. The aperture is large enough to permit passage of the bushing's cylindrical body, but not the flange, thereby allowing the flange to give hanging support for the body. The base of the engine is then placed on top of the flange, with the flange providing a cushioning support for the engine. A bolt is passed through the bore and sleeve, with its threaded end extending outwardly from the bore adjacent the support structure's lower side. A metal washer fitted over the bolt abuts the bushing's non-flanged end. By tightening a nut on the bolt's threaded end, the washer is forced towards the base of the engine, compressing the bushing. As the bushing compresses, its cylindrical body bulges outwardly and fills the space in and around the aperture. The sleeve provides support for the bushing. Since its length is shorter than the length of the bore in which it is received, the nut can be tightened until the sleeve is constrained between the engine and the washer. At that point, the bushing should be sufficiently compressed to provided a firm mounting support between the engine and support structure.
Obviously, it is critical that the bushing bulge outwardly if it is to provide firm mounting support. A problem, however, with using the typical bushing-sleeve combination in the previously described mounting process, is bushing end-splay as the bushing is compressed. End-splay is undesirable in that it causes failure in the bushing's ability to bulge properly. Such typically occurs when, during compression, the elastomeric cylindrical body portion of the bushing "flows" axially relative to the metal sleeve, with its end splaying outwardly relative to the washer. This particularly becomes a problem after a bushing has been compressed and relaxed several times. An important factor causing end-splay has been that a bushing's body, often, compresses non-uniformly because the body portion's non-flanged end fails properly to transmit mounting forces applied by the washer as a nut and bolt assembly is tightened.
To eliminate this problem, the present invention contemplates a modification of past-standard bushing-sleeve designs. The invention's bushing has a specially tapered, or chamferred, end which transmits axially displaced buckling forces in the bushing body. These forces torque the bushing's body outwardly, ensuring proper bulging as the bushing is compressed.
In addition, a preferred embodiment of the invention contemplates a metal sleeve fixed securely within the bushing. This prevents axial "flow" relative to the sleeve during compression, with the added feature of allowing the sleeve to provide better bulging support.
A general object of the present invention, therefore, is to provide a novel modification of a resilient bushing in combination with a metal sleeve for vibration-isolating mounting which offers the features and advantages outlined above.
More specifically, an object of the invention is to provide a bushing specially configured to cause a buckling torque in the bushing's body, thereby directing the bushing to "bulge" outwardly during axial compression.
Still another object of the invention is to provide, in such a combination, a metal sleeve which is fixed within the bushing so as to enable the sleeve to give improved bulging support to the bushing during compression.
A further object of the invention is to provide a bushing-sleeve combination of the type outlined which reduces fatigue wear in the bushing, thereby ensuring a longer usable life.
These and other objects and advantages which are attained by the invention will become more fully apparent as the following description is read in conjunction with the accompanying drawings.